Currently, demand for data communication is increasing in a mobile communication system. Various technologies achieving the high frequency utilization efficiency have been proposed with the increase in data communication.
One of the technologies capable of enhancing the frequency utilization efficiency is OFDMA (Orthogonal Frequency Division Multiple Access) in which a modulation scheme for communication is OFDM (Orthogonal Frequency Division Multiplexing) and an access scheme is TDMA (Time Division Multiple Access) or FDMA (Frequency Division Multiple Access). OFDMA is a communication scheme achieving higher-speed data communication while a common radio interface is used in both an isolated cell and a cell area.
In HSDPA (High Speed Downlink Packet Access) of a W-CDMA (Wideband-Code Division Multiple Access) mobile communication system, a scheduling method for an OFDMA system has been proposed in which a communication terminal device indicates a CQI (Channel Quality Indicator) for every subcarrier indicative of a downlink channel condition to a base station device so that the base station device performs packet scheduling based on the CQI for every subcarrier indicated by each communication terminal device (see, for example, Non-patent Document 1).
Similarly, an invention is disclosed in which a communication terminal device evaluates each downlink channel condition (frequency characteristics) upon scheduling of transmission data in an OFDMA system using multiple subcarriers and indicates the channel condition that is quantized to a base station device using an uplink feedback channel so that the base station device determines subcarriers to be allocated to each communication terminal device based on the indicated information (see, for example, Patent Document 1).
As a channel-quality feedback method for an OFDMA system, a method has been proposed in which a receiver selects multiple subcarriers having high channel qualities and indicates information indicative of the subcarriers and an averaged value of the channel qualities of the subcarriers to a transmitter so that the amount of feedback information is reduced to prevent overhead in reverse link from a communication terminal device to a base station device (see, for example, Patent Document 2).
Additionally, another method for an OFDM system has been proposed in which a receiver specifies carriers having bad channel qualities and indicates frequency information concerning the specified carriers or the numbers of the specified carriers to a base station so that the carriers having the bad channel qualities are not used (see, for example, Patent Documents 3 and 4).
Patent Document 1: Japanese Unexamined Patent Application, Fast Publication No. 2005-130491
Patent Document 2: Japanese Unexamined Patent Application, Fast Publication No. 2004-208234
Patent Document 3: Japanese Unexamined Patent Application, Fast Publication No. 2001-148682
Patent Document 4: Japanese Unexamined Patent Application, Fast Publication No. 2004-147068
Non-patent Document 1: “Comments on frequency scheduling and joint power and rate optimization for OFDM”, 3GPP, TSG RAN WG1 Meeting #29, R-02-1321, November, 2002